Numerous types of mats can accomplish stabilization and protection to underwater pipes and other seabed installations in off shore applications. Hydrodynamic forces, which are generated by the bottom currents and waves, create a need for a stabilization technique, such as a seabed mat. Prevention of erosion of the adjoining seabed is also another benefit created by seabed mats. Examples of articulated mats, their components, and their uses are given in U.S. Pat. Nos. 5,722,795, 5,944,449 and 5,443,329.
Concrete has typically been used as the covering of choice because of its strength and strong resistance to the action of natural types of water. However, many underwater pipelines are covered with a thin-filmed epoxy coating that is used as a protection system. If this epoxy coating is scratched, the pipeline is subject to corrosion. Therefore some mats have utilized pads in conjunction with an articulated mat in an effort to prevent the concrete from scratching or damaging the epoxy coating of the underwater pipelines. Additionally, cathodic protection is utilized as a maintenance system to prevent corrosion of the underwater pipelines.
The structure of prior art mats cause various problems in their use due to their closed cell design and inability to alter or vary the existing mat at the location of installation as shown in U.S. Pat. Nos. 5,722,795 and 5,944,449. The closed cell design on other abrasive resistant articulated mats provides an increased and unnecessary surface area abutting with the underwater pipeline or other seabed installation, thereby increasing the possibility of damage occurring to the underwater pipeline or seabed installation and decreasing the effectiveness of any accompanying cathodic protection system. The closed cell design also creates unnecessary weight on the mat, which greatly increases the difficulty of installing the product. Finally, the prior art does not provide for a means of modification of the mat at the installation location, in order to accommodate various situations, such as pipeline valves.
There is a need in the art for an abrasive resistant articulated seabed mat that is lighter weight and thus easier to install and also provides for a significant decrease in the surface area abutting the underwater structure thereby decreasing the possibility of the mat damaging the structure and maximizes the use of any cathodic protection system. There is also a need for an abrasive resistant articulated seabed mat that is capable of modification at the location of installation in order to accommodate various situations.
The present invention provides for an abrasive resistant open cell articulated seabed mat. The mat is made up of concrete blocks which each have a single square opening formed from the upper portion of the block through the center and continuing to the lower portion of the block. The top and bottom surface of the block is flat. One of the flat surfaces, preferably the surface adjacent the protected material, contains a solid abrasive resistant pad attached to the block.
The abrasive resistant pad is designed with an opening to match the opening on the block and with upwardly extending posts, which serve as the contact point between the concrete mat and the underwater pipeline. The structure of the pad and the open cell structure of the block, allows water to freely circulate between the mat and the pipeline. This combination of the open cell structure of the block and the structure of the abrasive resistant pad significantly reduces the surface area of the mat that actually abuts with the underwater pipeline or other structure. This decreases the possibility that the mat will damage the underwater pipeline or other structure. Additionally, if a cathodic protection system is utilized to provide additional protection to the underwater pipeline or structure, the combination of the open cell structure of the block and the structure of the abrasive resistant pad allows for a maximum utilization of any cathodic protection.
The abrasive resistant pad is attached to the surface of the block by a plurality of self-locking dowels extending downward from the pad. The entire pad is comprised of a homogeneous material. Although the pad could be made from various materials, the preferred embodiment of the pad is composed of a high-density polyethylene, although other substances such as low-density polyethylene, polyvinyl chloride, nylon or other mixtures thereof could be utilized. Each block contains apertures in its top surface, which receive the self-locking dowels located on the pad and serves to attach the pad to the block. An adhesive may also be utilized within the apertures, which receive the self-locking dowels to provide additional support for maintaining the pad in place on the top surface of the block.
The open cell design of the present invention allows the mat to be placed into the water more easily, especially in situations where large waves are present on the water""s surface. By allowing water to flow through the open cell design of the block, the blocks are able to be placed more accurately while the divers orienting the mats into place are exposed to less dangerous conditions. Other closed cell articulated seabed mats thwart vertical movement of water through the mat and therefore, are much more difficult to place in deep columns of water. Additionally, in situations where the mat has to be pulled up after placement to be reset, the amount of water to be displaced in a closed cell seabed mat is significantly greater than the amount displaced by an open cell.
The open cell design of the mat also allows for the open areas, to be filled with sand or other natural materials if desired. If suspended sediment is in the current, it is allowed to drop into the open cell design and thus provides additional roughness and stability to both the mat and the pipeline.
The present invention also allows for the size of the mat to be dynamically altered at any time, including the site of installation. The concrete blocks, which make up the mat, contain perpendicular apertures extending therethrough on each side of the block. The apertures are placed so as to allow a cris-crossing of cables through the block without intersecting. To form a mat, the blocks are aligned in a rows and columns wherein each column is substantially parallel with the other columns and wherein each row is substantially parallel with the other rows. A flexible cable is laced through the perpendicular apertures of each block. A single cable is used to attach two columns of blocks. The end pieces of cable, extending from the end of the adjacent columns of blocks, are extended so as to form a loop, utilized when handling the mat. Each of the end pieces of cable is connected with the cable extending from the end block on the adjacent column of blocks with a non-corrosive compression sleeve. The cable extending from the opposite end of the column of blocks also forms a loop.
A sleeve is placed on the cable next to the end block of each column. The loop extending from each of the columns is used for handling of the mat. The placement of the compression sleeves next to the apertures of the blocks, serve to hold the blocks securely in a column. Once the compression sleeve is placed in its proper location, it is closed or crimped together. The compression sleeve must be sufficiently large enough to prevent slipping into the aperture of the block.
The rows of the mat are connected in the same fashion as the columns, with one piece of cable connecting two rows. However, since typically all four sides of the mat will not be utilized while handling, the cables on the rows can be pulled tight with only one compression sleeve connecting the end pieces of cable extending from the end of the two rows.
The ability of the present invention to be altered as needed allows for great flexibility for the manufacturer and the consumer of the mat. A manufacturer is capable of making any size mat that a customer requires. Additionally, a customer is capable of modifying the size of the mat at any time, including at the site of installation. This allows the consumer to address unexpected needs that may arise during the installation of the mat.
The present invention also allows for the creation and manufacturing of the blocks to be separated from the attachment of the pads. This provides the customer the ability to replace pads, which may become damaged during transport or in the installation process. The consumer also has the ability to place the needed pads at the site of installation.